Method for preparing microcapsules by double emulsion

Abstract

The present invention relates to a method for preparing solid microcapsules, comprising the steps of: a) adding under agitation a composition C1 comprising at least one active material to a cross-linkable liquid composition C2, wherein the active material is an additive to be used in the oil industry, composition C1 and composition C2 being immiscible with each other, so that a first emulsion is obtained, said first emulsion comprising droplets of composition C1 dispersed in composition C2, b) adding under agitation the first emulsion obtained in step a) to a liquid composition C3, composition C3 and composition C2 being immiscible with each other, so that a second emulsion is obtained, said second emulsion comprising droplets dispersed in composition C3, c) loading the second emulsion obtained in step b) in a mixer which applies a homogeneous controlled shear rate to said second emulsion, said shear rate being from 1 000 s−1 to 100 000 s−1, so that a third emulsion is obtained, said third emulsion comprising droplets dispersed in composition C3, and d) cross-linking the droplets obtained in step c), so that solid microcapsules dispersed in composition C3 are obtained.

1 . Method for preparing solid microcapsules ( 20 ), comprising the steps of:
 a) adding under agitation a composition C1 comprising at least one active material to a cross-linkable liquid composition C2,
 wherein the active material is an additive to be used in the oil industry, composition C1 and composition C2 being immiscible with each other, so that a first emulsion is obtained, said first emulsion comprising droplets ( 1 ) of composition C1 dispersed in composition C2, 
   b) adding under agitation the first emulsion obtained in step a) to a liquid composition C3,
 composition C3 and composition C2 being immiscible with each other, so that a second emulsion is obtained, said second emulsion comprising droplets ( 5 ) dispersed in composition C3, 
   c) loading the second emulsion obtained in step b) in a mixer which applies a homogeneous controlled shear rate to said second emulsion, said shear rate being from 1 000 s −1  to 100 000 s −1 ,
 so that a third emulsion is obtained, said third emulsion comprising droplets ( 10 ) dispersed in composition C3, and 
   d) cross-linking the droplets ( 10 ) obtained in step c),
 so that solid microcapsules ( 20 ) dispersed in composition C3 are obtained. 
   
     
     
         2 . Method according to  claim 1 , wherein the active material is solubilized into composition C1. 
     
     
         3 . Method according to  claim 1 , wherein the active material is dispersed in the form of solid particles into composition C1. 
     
     
         4 . Method according to  claim 1 , wherein the active material is an additive to be included in lubricants, lubricating base oils, fuels, bitumens, or in the drilling fluids, sludges or muds, or an additive to be used in oil exploration/production. 
     
     
         5 . Method according to  claim 1 , wherein composition C2 comprises at least one monomer or polymer, at least one cross-linker and at least one initiator of polymerization. 
     
     
         6 . Method according to  claim 1 , wherein the viscosity of composition C2 at 25° C. is from 500 mPa·s to 100 000 mPa·s. 
     
     
         7 . Method according to  claim 1 , wherein the viscosity of composition C2 is higher than the viscosity of composition C1. 
     
     
         8 . Method according to  claim 1 , wherein during step a), the volume of composition C1 to the volume of composition C2 ratio is from 1:10 to 10:1. 
     
     
         9 . Method according to  claim 1 , wherein the viscosity of composition C3 at 25° C. is higher than the viscosity at 25° C. of the first emulsion obtained in step a). 
     
     
         10 . Method according to  claim 1 , wherein during step b), the volume of the first emulsion to the volume of composition C3 ratio is from 1:10 to 10:1. 
     
     
         11 . Method according to  claim 1 , wherein the mixer used in step c) is a Couette-geometry mixer, comprising two concentric cylinders, an outer cylinder of inner radius R o  and an inner cylinder of outer radius R i , the outer cylinder being fixed and the inner cylinder being rotating with an angular velocity ω. 
     
     
         12 . Method according to  claim 11 , wherein the angular velocity w of the rotating inner cylinder is over than or equals to 30 rad·s −1 . 
     
     
         13 . Method according to any one of  claim 11  or  12 , wherein the gap d=R o  −R i  between the two concentric cylinders is from 50 μm to 1 000 μm. 
     
     
         14 . Method according to  claim 1 , wherein during step d), the cross-linking is carried out by submitting the double droplets ( 10 ) obtained in step c) to a source of light, able to initiate the cross-linking of composition C2. 
     
     
         15 . Series of solid microcapsules ( 20 ), said microcapsules ( 20 ) being obtainable by the method of  claim 1 , each microcapsule ( 20 ) comprising:
 a core comprising a composition comprising at least one active material as defined in  claim 1 , and   a solid cross-linked shell surrounding said core,   wherein the standard deviation of microcapsule diameter distribution is below 25% or below 1 μm.   
     
     
         16 . Series of solid microcapsules ( 20 ) according to  claim 15 , wherein the average diameter of the solid microcapsules ( 20 ) is less than or equal to 10 μm. 
     
     
         17 . Series of solid microcapsules ( 20 ) according to  claim 15 , wherein each solid microcapsule ( 20 ) is surfactant-free. 
     
     
         18 . Series of solid microcapsules ( 20 ) according to  claim 15 , wherein each solid microcapsule ( 20 ) is water-free. 
     
     
         19 . Composition comprising a series of solid microcapsules ( 20 ) according to  claim 15 , and a lubricating base oil. 
     
     
         20 . Method for releasing an active material, comprising a step of applying a mechanical shear stress to a composition comprising a series of solid microcapsules ( 20 ) according to  claim 15 .